My long-term objective is to understand how neural processing in extrastriate visual cortex contributes to visual perception and visually guided behavior. The proposed research will focus on an extrastriate pathway in monkeys which is thought to be primarily involved in the analysis of visual motion. This pathway begins in striate cortex and continues through the Middle Temporal area (MT) and the Medial Superior Temporal area (MST) before reaching visuomotor regions of the parietal lobe that process information in more complex ways. Insight gained from these studies in rhesus monkeys may well be applicable to the human visual system since the visual and oculomotor capabilities of rhesus monkeys are known to be very similar to those of man. In addition, recent neurological findings suggest that a specific cortical pathway for visual motion exists in humans as well. Experiments will be carried out in awake, behaving monkeys trained to perform simple visuomotor and visual detection tasks. 1) Behavioral experiments will test the effects of chemical lesions of MT on a monkey's ability to detect visual motion and spatio-temporal contrast. This line of investigation should produce firm behavioral data concerning the functional role of MT in visual perceptions. 2) Physiological experiments will concentrate on a quantitative analysis of visual and visuomotor responses of single neurons in MST. Particular attention will be paid to neurons in MST which are known to fire in response to visual stimulation and in response to smooth pursuit eye movements. Interactions of these inputs will be examined, and the neural signals which drive the pursuit-related response will be studied. These experiments will complement previous studies of neuronal responses to visual motion in striate cortex, MT, and the parietal lobe, and will thus complete an initial physiological survey of this cortical motion pathway.